Okay, set it on any campaign you want and put it on easy. Then, get a PUMP shotgun and leave the saferoom. When you come upon a witch turn your light off and go up BEHIND it. If you go in front of it, you're not gonna get it. When behind it, aim for the spot just above  the middle on her back. Make sure this can also hit a little of her neck. If you do this and miss, just do it again, only aim higher. Make sure its on EASY!!! It also works on L4D2 only use the pump or the black shotgun.

Thank you, goodbye!